This project is devoted to the analysis of the induction and expression of cell-mediated immunity (CMI) in the lungs. To this end two infectious disease models have been chosen, one of which, Listeria monocytogenes, produces an acute infection and the other, Mycobacterium tuberculosis, a chronic infection. It has been established that these lung infections induce a state of CMI and it is now intended to analyze the expression of CMI. Animals immunized via the lungs are more resistant to pulmonary re-infection. This phenomenon is attributable partly to non-specific resistance which is vested in activated macrophages and partly to specifically sensitized lymphocytes. It is suggested that intrapulmonary lymphoid tissue may play an important role as the location of a subpopulation of non-recirculating lymphocytes which are limited in distribution to those tissues containing antigen. The presence of macrophage activation will be monitored by the resistance of the lung to airborne challenge with heterologous organisms. The influx of mobile macrophages into the lungs will be measured by established radio-labelling techniques. Lymphocytes will be isolated from the lungs by velocity sedimentation and dermal delayed-type hypersensitivity (DTH) will be analyzed, using a novel technique for measuring DTH. By use of these procedures the distinctive contributions of activated macrophages and sensitized lymphocytes to the lung defenses will be clarified.